Traditionally, ethylene and α-olefins can be polymerized or copolymerized, using catalytic systems containing a transition metal, such as titanium, and an organometallic compound, such as alkylaluminum. More recently, homogeneous catalytic systems, such as, for example, metallocene bis(cyclopentadienyl) titanium dialkyl in the presence of trialkylaluminum and water, showed active for ethylene polymerization. The German patents 2,608,863 and 2,608,933 show the use of this type of catalytic system in the ethylene polymerization.
Thus, metallocene-type complexes are increasingly becoming important as a new generation of catalysts for preparation of polyolefins. By metallocene, it is understood transition metal complexes containing one or more π ligands of the type cyclopentadienyl, substituted or not, such as, for example, “sandwich”- or “half-sandwich”-type compounds, i.e., metal complexed to two π ligands or one π ligand, respectively. These complexes become active in polymerization of olefins when activated by an organometallic compound also known by cocatalyst. Known examples of cocatalysts, widely used in the activation of metallocenes, are the aluminoxanes, particularly methylaluminoxane. The European patent EP 0035242 informs a process for preparation of ethylene polymers in the presence of catalytic systems of the type activated metallocenes by aluminoxane. Additional learning of homogeneous catalytic systems comprising metallocene and aluminoxane are showed in the patent EP 0069951.
Comparatively to the conventional Ziegler-Natta catalytic system, the homogeneous metallocene catalytic systems not only present high catalytic activities, but also capacity to control the properties of the polyolefins as function of the compounds used in its synthesis and reaction conditions. Nevertheless, these catalytic systems present the disadvantage to use a great excess of aluminoxanes, in relation to the content of transition metal of the catalyst, to yield acceptable productivities. Due to the high cost of the aluminoxanes and also to the necessity of extra work of purification of the polymers obtained, the production of polyolefins in industrial scale, based on such catalytic systems, generally becomes anti-economical. Besides, the use of toluene, which is commonly used in the formulation of aluminoxanes, particularly methylaluminoxane (herein referred as MAO), is increasingly becoming highly undesirable for toxicological reasons in relation to the field of application of the polyolefins and for storage stability reasons of the highly concentrated formulations (tendency to gel formation).
Other disadvantage of these homogeneous catalytic systems is that the polymer obtained presents medium size of small particle and apparent low density. When used in gas phase or slurry processes, there is a tendency to dirt the reactor through the formation of polymer deposits in the surface of the reactor or stirrer walls.
Thus, in the attempt to overcome the problems mentioned above, such homogeneous catalytic systems were supported, as already known in the state-of-art. A supported metallocene catalytic system is described in the U.S. Pat. No. 5,086,025 where, the homogeneous metallocene is deposited on a silica containing aluminoxanes, which was obtained by the water reaction absorbed in silica with trialkylaluminum. Different methods to support metallocene catalysts are described, for example, in the patents WO 95/07939, WO 87/03889, WO 94/28034, EP 206794 and EP 250600, where derivatives of aluminoxane compounds are used as cocatalysts. In addition to aluminoxane compounds, organoboron compounds can also be used as catalysts and the patents WO 91/09882, WO 94/03506, EP 628574 and WO 95/15815 teach how to use them along with the metallocene catalysts in support process. In addition to the question of cost associated to the use of aluminoxane and organoboron compounds, the procedure to prepare such supported catalysts is complicated and expensive.
In addition to the use of supported bimetallic catalysts, the state-of-art recognized that the benefits can be obtained along with technologies of metallocene catalysts and Ziegler-Natta in the production of low pressure polyolefins. Such preparations, generally known as bimetallic catalytic systems or bimetallic catalysts, refers to two more catalytic compounds used in combination with, at least, an activator and, optionally, with a support, which are useful in the polymerization of olefins.
The U.S. Pat. No. 5,525,678 informs a supported catalytic composition comprising a magnesium-based compound and the mixture of an activated metallocene compound by aluminoxane and a non-metallocene compound, such as halocarbons or alkoxydes of Ti or V. Such composition is able to produce polymers with broad or bimodal molecular weight distribution (herein referred as MWD) in a single reactor, seen the present different compounds present different responses to H2.
Patent EP 0790259 A1 shows that it is possible to obtain monomodal polyolefin resins and broad MWD using, for this, a supported catalyst containing isomeric mixture of metallocenes with bridge, of the type (IndH4)2R″MQ2, where Ind is the indenyl group, substituted or not, R″ is the bridge between indenyl groups and can be a dialkylgermanium, dialyklsilicium or siloxane group, Q is a radical of the alkyl or aryl type and M is the transition metal chosen among Ti, Zr or Hf. This isomeric mixture of metallocenes needs to be activated, previously to support, by aluminoxane.
Patent EP 1403288 A1 presents the preparation of supported catalyst containing the mixture of hafnocene and other metallocene or non-metallocene compound to obtain polyolefin with broad or multimodal MWD where, the hafnocene produces a high molecular weight fraction and the other metallocene or non-metallocene compound produces the low molecular weight fraction. This catalyst containing the mentioned mixture must be activated by ionization agents and with non-coordinating capacity, such as borates or aluminates.
U.S. Pat. No. 6,664,351 claims the production of ethylene copolymers with broad MWD from a mixture of racemic isomers and meso of a stereorigid metallocene catalyst supported in an organic support and activated by aluminoxane-type compounds.
U.S. Pat. No. 6,384,144 from Basell, claims the production of a reactor blend obtained from a mixture of catalytic systems comprising transition metal compounds form the beginning of the Periodic Table (groups 3 to 7 of the Periodic Table) and transition metals from the end of the Periodic Table (groups 8 to 11 of the Periodic Table). This mixture is able to produce at least two types of linear polyethylenes with different contents of branching, after activation by alumonoxane-based cocatalysts.
Several catalytic systems have been used to obtain the polyethylene with high molecular weight, presenting the final polymer an extremely high molecular weight. Polyethylene of this type presents a molecular weight ranging from 10 to 20 times the molecular weight of a HDPE. This polymer usually is known as high and ultra-high molecular weight polyethylene, called henceforth HMWPE and UHMWPE, respectively. HMWPE shows viscometric molecular weight (herein referred as Mv) that may range between 500,000 and 2,500,000 g/mol, while UHMWPE shows Mv that is above 2,500,000 g/mol.
The commercially produced UHMWPE in moderate pressures and temperatures, is traditionally obtained by Ziegler-Natta catalyst, as showed in the patents U.S. Pat. No. 5,880,055 and BR 9,203,645A. Other characteristic of these polymers is that they show similar properties to conventional HDPE which is the broad distribution of molecular weight (herein referred as MWD), with the Mw/Mn value in the range from 4 to 20.
The LG Chem., in its patent WO 06080817, claims to obtain polymers presenting a fraction of high molecular weight of 1,000,000 g/mol and with high amount of comonomer incorporated, obtained from a supported catalyst containing a mixture of metallocenes with transition metals of the group 3 of the Periodic Table. Such catalysts are activated by aluminoxane or organoboron compounds to obtain polymers that show MWD ranging between 5 and 30.
The patent CA 2281559, in its turn, shows that it is possible to obtain high and ultra-high molecular weight polyolefins from catalysts containing a mixture of metallocene and Ziegler-Natta supported in styrene polymers and copolymers.
The U.S. Pat. No. 6,384,144 comments that the polymerization process can occur in liquid or gaseous phase, but the preference is by the liquid phase process.
U.S. Pat. No. 6,664,351 also comments that the catalyst can be used not only in the gas phase, but also in the liquid phase. Patent EP 00676418 A1, in its turn, talks about the polymerization process is preferably performed in the gas phase.
Therefore, references in the state of the art, considered alone or in combination, do not describe nor suggest a method to prepare supported bimetallic catalysts destined to polymerization reactions of ethylene and copolymerization of ethylene with α-olefins from a mixture of two transition metals supported in a catalytic support and an activator with base of organometallic compounds of the groups 2 or 13 of the Periodic Table and that are not aluminoxanes or organoboron, where the first transition metal compound is preferably a transition metal complex of the groups 4 or 5 of the Periodic Table containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, and the second transition metal compound is preferably a transition metal complex of the groups 4 or 5 of the Periodic Table containing ligands like halides, alkyl, alkoxy or monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, and that produce ethylene homopolymers and copolymers with α-olefins, with high molecular weight (HMWPE) and of ethylene homopolymers and copolymers with α-olefins, with ultra-high molecular weight (UHMWPE), with broad molecular weight distribution, used in slurry, bulk and gas phase processes, as described and claimed in the present application.
The obtained ethylene homopolymers and ethylene copolymers with α-olefins show high molecular weight in the presence of mentioned supported bimetallic catalysts. More specifically, the present invention relates to a process for preparation of supported bimetallic catalysts, from a mixture of two transition metals of the groups 4 or 5 of the Periodic Table supported on a catalytic support and an organometallic compound of the groups 2 or 13 of the Periodic Table, and which are not aluminoxanes or organoboron compounds, where the first transition metal compound is preferably a transition metal complex of the groups 4 or 5 of the Periodic Table containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, and the second transition metal compound is preferably a transition metal complex of the groups 4 or 5 of the Periodic Table containing ligands like halides, alkyl, alkoxy or monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, for ethylene homopolymerization and ethylene copolymerization with α-olefins, from a catalytic support prepared in the absence of activators such as aluminoxanes or organoboron based compounds. More specifically, the present invention also relates to a process to produce ethylene homopolymers or ethylene copolymers with α-olefins, with high molecular weight and ultra high molecular weight, such as HMWPE and UHMWPE, with broad MWD, in the presence of the mentioned supported bimetallic catalysts supported on a catalytic support and prepared in the absence of activators such as aluminoxanes or organoboron based compounds. The invention also relates to the catalytic support prepared in the absence of activators such as aluminoxanes or organoboron based compounds, to the supported bimetallic catalysts obtained from a mixture of 2 or more metallocene catalysts based on transition metal of the groups 4 or 5 of the Periodic Table, containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, or a mixture of Ziegler-Natta catalyst based on transition metal of the groups 4 or 5 of the Periodic Table and a metallocene catalyst based on transition metal of the groups 4 or 5 of the Periodic Table, containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, to the ethylene homopolymers and ethylene copolymers with α-olefins, with high molecular weight and ultra high molecular weight, such as HMWPE and UHMWPE, and broad MWD, and to the polymerization processes to produce ethylene homopolymers and ethylene copolymers with α-olefins with high molecular weight and ultra high molecular weight in presence of the mentioned supported bimetallic catalysts and in the absence of activators such as aluminoxanes or organoboron based compounds.